This invention relates to a filter apparatus and method of its operation, particularly to a pressure filter and method for extracting liquids from slurry fluids and for producing a substantially-dry filter cake of the solid materials present in such slurry fluids.
In many industrial processes and other applications where a slurry of solids and liquids is produced, it becomes necessary to filter the slurry solids from the liquids so that these materials may be efficiently utilized or, alternatively, disposed in an environmentally safe manner. To separate the solids from the liquids, a filter apparatus, such as a pressure filter, is often employed. Known pressure filters may include one or more pairs of filter plates capable of relative motion. As an example, in a pressure filter having only a single pair of plates, the inlet plate is generally adapted for receiving the slurry, while the filtered liquids, called the filtrate, are collected by means of the outlet plate, which also provides the requisite support for a filter medium, positioned between the filter plates. This arrangement permits a filtration chamber to be defined by the inlet plate and the filter medium when the plates are pressed together. In the usual production cycle of such a filter, slurry is introduced into the filtration chamber under pressure through an inlet port, whereby it distributes itself throughout the chamber. After the filtration chamber is filled with slurry, the filter executes a series of programmed operations, namely, washing the contents of the chamber in a particular manner, as well as pressurizing the chamber, e.g., with compressed air, to force the liquids from the slurry through the filter medium, leaving the slurry solids, consolidated in a substantially dry filter cake, within the chamber. The slurry liquids are collected and are either used or disposed in an appropriate manner. The chamber is then opened, allowing the filter cake to be removed therefrom.
Known pressure filters are capable of successfully treating a wide variety of slurries. However, the use of such filters has shown to be impractical for filtering certain difficult-to-filter slurries, such as certain modified starch, pigment, and molybdenum sulfide slurries. These slurries have proven to be difficult to filter, either because they contain fine particles, e.g., fines on the order of 0.5–10 microns, or because they include compressible solids. In either case, the filter cake being formed In a filtration chamber of a conventional pressure filter may become virtually impermeable to liquids being forced through the slurry solids using gases under commercially available pressures on the order of 100 psi. As a result, the time required to produce a substantially dry filter cake for these types of difficult-to-filter slurries drastically increases, making it impractical to use known pressure filters for treating such slurries. One solution may be to increase the pressure of the gas(es) used to force the liquids from the forming filter cake. However, this alternative proves to be cost-prohibitive because it requires the use of additional equipment and a substantial amount of energy to continuously maintain large quantities of compressed gas at the requisite high pressure.
Thus, a need arises for a pressure-filter apparatus capable of efficiently treating difficult-to-filter slurries, such as the types of slurries described above.
It is also desirable to provide a pressure-filter apparatus that is energy-efficient and is capable of extracting the slurry liquids to produce a substantially dry filter cake in a minimum amount of time.